1. Field of the Invention
The present invention relates to a television picture coding device comprising in particular:
(A) a motion estimating stage; PA1 (B) a control circuit for controlling said motion estimation; PA1 (C) a coding stage; PA1 (D) a multiplexing stage. It also relates to a corresponding decoding device allowing decoding of the signals thus encoded. PA1 (A) the motion estimating stage comprises: PA1 (B) the motion estimating checking stage comprises: PA1 (C) the coding stage (120) comprises a spatial coding circuit; and PA1 (D) the multiplexing stage is arranged to ensure the multiplexing of the output signals of the coding stage and of the motion estimating stage.
The invention also relates to a system incorporating such devices and intended for the transmission of television pictures via a digital channel having a limited passband which implies a processing operation for reducing the quantity of information components to be transmitted. It finally relates to transmission and receiving stages of such a system.
The transmission or the recording of television pictures in digital form actually requires, if video signals are transmitted in the form they are in after digitizing, a passband which is eight times larger than for analog signals. Such a digital transmission via a narrow-band channel necessitates a very important reduction of the binary rate necessary for the presentation of the pictures.
2. Description of Related Art
The techniques rendering this rate reduction possible can employ the correlation present within each picture. The U.S. Pat. No. 4,394,774 discloses an example of a block-wise encoding technique, based on the discrete cosine transform, which utilizes this spatial correlation very efficiently. However, for an additional reduction of the rate, the correlation existing between pictures must be taken into account, more specifically in the still zones or in the moving zones.
Predictive techniques with motion compensation which allow the reduction of the rate up to almost 1 bit per picture element (pixel), without disturbing degradation of the quality of the decoded pictures, are also known: a loop is, for example, made operative from picture to picture, that is to say that, to transmit a block of each picture, either the block itself or the difference between this block and a block originating from the preceding encoded and decoded picture are encoded. Consequently, this technique implies that, for decoding a picture in the receiver, it is necessary to have the disposal of this encoded and decoded preceding picture.
This type of coding can therefore not be used to record picture sequences on a video recorder, in which one of the essential properties is the possibility to quickly scan the magnetic tape while displaying the pictures. Actually, this characteristic necessitates the decoding of a picture on the basis of data corresponding to this picture, and these data only, which excludes any technique in which any type of picture repetition is used.